I save rewrites for those days when I want to write but I'm feeling stuck. Rather than turn writing into a chore and try to pummel the pages out of me, I go back and tweak scenes, rewrite passages or pages, or fix things I wanted to fix. This is also where I usually go back and strengthen certain hints that turned out later to be a major cool thing.
For instance, in one story, early chapters showed the protagonist working with these hand-blown glass jars. At the time I wrote that scene, they were just something for her to be putting on the shelves in her store. When I later had the protagonist trapped in the ruins of a house with an evil spirit, I had to stop and think about how to get her out of it. I had established some critical facts about her personality and situation that made her unable to exorcise the spirit entirely or otherwise banish it, but she plainly couldn't let it go. Which sort of left me with trapping it. And that made me think of the glass jars. So I wrote on, with her trapping the spirit in a glass *bottle*. The next time I got stuck, I had a note tacked up over my desk to fix this ("glass jars = bottles") and was able to work on that. I changed the jars to bottles, made the description of them longer and more intricate, and threw in additional references to them from time to time.
It warms me up, gets the creative motor running so I can get past the stuck bits. But I don't stop where I am and go back to rewrite. Never interrupt a flow.